1. Field of the Invention
The present invention relates to a residual gas removing device in a gas supply apparatus used in a semiconductor manufacturing facility, and more particularly, to a residual gas removing device for removing a WF6 gas remaining in the gas lines of the gas supply apparatus.
2. Description of the Related Art
In general, a tungsten silicide film is grown via a reaction between dichloro silane and WF6 gas in a so-called Diclor Siliden (DCS) WSix process. The tungsten silicide WSix film is formed and patterned on a polysilicon film, thereby forming low resistance bitlines and wordlines which are connected in parallel to the polysilicon layer.
In the course of fabricating such wiring, a problem has occurred in which the adhesion force of the WSix film on the polysilicon film is reduced and the two films are subject to delamination, whereby the two films come apart due to a difference in stress between the two films. Delamination occurs, for example, during a heat treatment performed in a BPSG reflow process in an environment having a temperature of 830° C. and a pressure of 30″. Delamination may also occur during an SiN deposition process having a temperature of 1100° C.
Accordingly, it is necessary to prevent such a delamination phenomenon from occurring during the formation of the WSix film. One way to prevent the delamination is to reduce the tungsten-rich environment during the WSix formation process. If the WF6 gas is removed after the main deposition step, the ratio of tungsten (W) and silicon (Si) is changed and the amount of tungsten can be reduced. In other words, the tungsten-rich (W-rich) phenomenon can be prevented by removing WF6 gas after the main deposition process, thereby resulting in the formation of a low-stress film and being able to control defects in the films.
FIG. 1 is a schematic view showing the structure of a gas supply apparatus in a conventional semiconductor fabricating facility. The gas supply apparatus includes a main gas can 10, which can supply various gases, for example, dichloro silane (DSC) gas, and a WF6 gas supply can 20 to supply a WF6 gas.
The first valve group 30, comprising valves SV2-SV8, removes air in each of the supplied gas lines. The second valve group 40 comprises eight up-stream valves UV1 to UV8. The second valve group 40 serves to shut off the WF6 gas can 20, or any of the various gases from the main gas can 10, during the change of a mass flow controller (MFC) group 60. The controller group 60 comprises mass flow controllers (MFC) MF1 to MF8 to control gas pressure in each of the gas lines. The third valve group 50 comprises eight purge valves PV1 to PV8 to purge gases remaining in each of the gas lines during changes in the MFC group. The fourth valve group 70 comprises eight vent valves VV1 to VV8, to vent the residual gas in each of the gas lines. The fifth valve group 80 comprises eight down-stream valves DV1 to DV8 to shut off gases from the gas lines connected to the chamber 90, thereby preventing the gas from flowing outside during the change of the mass flow controllers (MFC). The low stress valve 100 regulates (i.e., supplies or cuts off) gases being supplied from MF5 to MF8 of the MFC group 60.
The gas supply apparatus further includes inner needle vent valve 91 and outer needle vent valve 92 at the entrance of the chamber 90. When the inner needle vent valve 91 is full opened, WSix film uniformity is controlled according to whether the outer needle vent valve 92 is opened or closed, and the thickness of WSix film is controlled by the deposition time. The shower head of the inner needle vent valve 91 is divided into an inner zone and an outer zone, and the amount of gas out-flowing through each of the inner zone and the outer zone is controlled to ensure film uniformity.
For completeness, MPVA and MPVB identify main purge valves A and B, and MVVA and MVVB identify main vent valves A and B, respectively.
This conventional gas supply apparatus has a problem in that the WF6 gas, which is used in a main deposition process, remains in the gas line 81 (i.e., the gas inlet line to the low stress valve 100), and then during a subsequent process, flows into the chamber 90 with a carrier gas such as argon gas (Ar) through the low stress valve 100. Because of this residual gas, the amount of tungsten is increased on a wafer surface (W-rich phenomenon), which in turn increases the stress between the films, causing delamination.